Turns out that with IC off, Poser Pro doesn't really know what to do with the skull cap. The blotchies are all gone, but only by virtue of the whole skullcap essentially becoming one big shadow. Essentially, the render has the "shadow" tracing the contours of the edge of the skullcap. Not what we want.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3